1. Field of the Invention
The purpose of this invention is to form wet-spun fibers by varying the rate of polymer coagulation through adjustments in non-solvent/solvent miscibility and precipitation strength to control internal morphology of the wet-spun fibers.
2. Description of the Related Art
As the microelectronics industry moves toward higher rates of data transmission, laminate materials with enhanced dielectric properties will be needed for high-speed multi-layer printed wiring boards (PWB's). Since composites are highly filled with reinforcing materials, fibers will play a significant role in lowering the overall dielectric constant of PWB's.
The development of polyimides possessing high solubility, optical transparency in the visible spectrum, and low dielectric constants has been studied.
One such polyimide, known as poly(6FDA-4BDAF), has been made from 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianydride (6FDA) and 2,2-bis 4-(4-aminophenoxy) phenyl!hexafluoropropane (4BDAF), and has the following formula: ##STR1## This polymer has a dielectric constant of 2.5 at 10 GHz.
However, the above-identified polymer has had little success in the area of fiber spinning. More specifically, fibers spun from the 6FDA-4BDAF polymer were reported as non-circular and containing large voids and/or a sponge-like texture that remained through heat treatment resulting in weak filaments. Therefore, successful production of solid core filaments from this polymer has not been achieved by these past attempts. Also, the resulting filaments exhibited low moduli (5GPa) and tenacity (0.2GPa).
Accordingly, there is a need for a process which enables control of fiber microstructure, enabling production of fibers having a tailored microstructure, including a solid core microstructure.
It is therefore an object of the present invention to provide a process that can control fiber morphology by varying the rate of polymer coagulation through adjustments in non-solvent/solvent miscibility and precipitation strength.
It is another object of the present invention to provide a process whereby the solvent utilized for spinning the fiber is selected based upon polymer solubility and solvent/coagulant miscibility such that the rate of coagulation can be controlled.
It is another object of the present invention to provide a process utilizing a solvent that is miscible in only one of the agents of the coagulating bath such that, by varying the ratio of the binary solution in the coagulation bath, greater control of the fiber structure is achieved by limiting the rate of coagulation.